rear axle leak

Hello everyone, I am still struggling with sourcing parts in the UK for my 2005 Sport Trac. This time I spotted a leak from the rear left axle oil seal, and took apart the axle from the diff in order to get to the leaky seal and remove it. Now I am stumped because I can't find a replacement...

unfortunately, since this economy went down, i got laid off by chrysler as an apprentice mechanic... i have a 03 explorer sport trac 4wd, and i've noticed when i did my shocks that my passenger side axle seal is leaking diff fluid... i checked the diff fluid level and it seems to be full...